Messages in this thread | | | From | "Alexander van Heukelum" <> | Subject | Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes | Date | Mon, 10 Nov 2008 22:44:18 +0100 |
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On Mon, 10 Nov 2008 07:39:22 -0800, "H. Peter Anvin" <hpa@zytor.com> said: > Ingo Molnar wrote: > > * Alexander van Heukelum <heukelum@fastmail.fm> wrote: > > > > hackbench is _way_ too noisy to measure such cycle-level differences > > as irq entry changes cause. It also does not really stress interrupts > > - it only stresses networking, the VFS and the scheduler. > > > > a better test might have been to generate a ton of interrupts, but > > even then it's _very_ hard to measure it properly. The best method is > > what i've suggested to you early on: run a loop in user-space and > > observe irq costs via RDTSC, as they happen. Then build a histogram > > and compare the before/after histogram. Compare best-case results as > > well (the first slot of the histogram), as those are statistically > > much more significant than a noisy average. > > > > For what it's worth, I tested this out, and I'm pretty sure you need to > run a uniprocessor configuration (or system) for it to make sense -- > otherwise you end up missing too many of the interrupts. I first tested > this on an 8-processor system and, well, came up with nothing. > > I'm going to try this later on a uniprocessor, unless Alexander beats me > to it.
I did the rdtsctest again for the irqstubs patch you sent. The data is at http://heukelum.fastmail.fm/irqstubs/ and the latency histogram is http://heukelum.fastmail.fm/irqstubs/latency_hpa.png
Greetings, Alexander
> -hpa -- Alexander van Heukelum heukelum@fastmail.fm
-- http://www.fastmail.fm - Same, same, but different...
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